Minimal Microscopic Heat Engine published in Phys. Rev. E

Experimental realization of a minimal microscopic heat engine

Experimental realization of a minimal microscopic heat engine
Aykut Argun, Jalpa Soni, Lennart Dabelow, Stefano Bo, Giuseppe Pesce, Ralf Eichhorn & Giovanni Volpe
Physical Review E 96(5), 052106 (2017)
DOI: 10.1103/PhysRevE.96.052106
arXiv: 1708.07197

Microscopic heat engines are microscale systems that convert energy flows between heat reservoirs into work or systematic motion. We have experimentally realized a minimal microscopic heat engine. It consists of a colloidal Brownian particle optically trapped in an elliptical potential well and simultaneously coupled to two heat baths at different temperatures acting along perpendicular directions. For a generic arrangement of the principal directions of the baths and the potential, the symmetry of the system is broken, such that the heat flow drives a systematic gyrating motion of the particle around the potential minimum. Using the experimentally measured trajectories, we quantify the gyrating motion of the particle, the resulting torque that it exerts on the potential, and the associated heat flow between the heat baths. We find excellent agreement between the experimental results and the theoretical predictions.

Guide to Building Optical Tweezers published in JOSA B

A step-by-step guide to the realisation of advanced optical tweezers

A step-by-step guide to the realisation of advanced optical tweezers
Giuseppe Pesce, Giorgio Volpe, Onofrio M. Maragò, Philip H. Jones, Sylvain Gigan, Antonio Sasso & Giovanni Volpe
Journal of the Optical Society of America B 32(5), B84—B98 (2015)
DOI: 10.1364/JOSAB.32.000B84
arXiv: 1501.07894

Since the pioneering work of Arthur Ashkin, optical tweezers (OT) have become an indispensable tool for contactless manipulation of micro- and nanoparticles. Nowadays OT are employed in a myriad of applications demonstrating their importance. While the basic principle of OT is the use of a strongly focused laser beam to trap and manipulate particles, more complex experimental setups are required to perform novel and challenging experiments. With this article, we provide a detailed step-by-step guide for the construction of advanced optical manipulation systems. First, we explain how to build a single-beam OT on a homemade micro- scope and how to calibrate it. Improving on this design, we realize a holographic OT, which can manipulate independently multiple particles and generate more sophisticated wavefronts such as Laguerre–Gaussian beams. Finally, we explain how to implement a speckle OT, which permits one to employ random speckle light fields for deterministic optical manipulation.

Longterm Influence of Fluid Inertia on Brownian Motion published in Phys. Rev. E

Longterm influence of fluid inertia on the diffusion of a Brownian particle

Longterm influence of fluid inertia on the diffusion of a Brownian particle
Giuseppe Pesce, Giorgio Volpe, Giovanni Volpe & Antonio Sasso
Physical Review E 90(4), 042309 (2014)
DOI: 10.1103/PhysRevE.90.042309
arXiv: 1402.6913

We experimentally measure the effects of fluid inertia on the diffusion of a Brownian particle at very long time scales. In previous experiments, the use of standard optical tweezers introduced a cutoff in the free diffusion of the particle, which limited the measurement of these effects to times comparable with the relaxation time of the fluid inertia, i.e., a few milliseconds. Here, by using blinking optical tweezers, we detect these inertial effects on time scales several orders longer up to a few seconds. The measured mean square displacement of a freely diffusing Brownian particle in a liquid shows a deviation from the Einstein-Smoluchowsky theory that diverges with time. These results are consistent with a generalized theory that takes into account not only the particle inertia but also the inertia of the surrounding fluid.

Stratonovich-to-Itô Transition published in Nature Commun.

Stratonovich-to-Itô transition in noisy systems with multiplicative feedback

Stratonovich-to-Itô transition in noisy systems with multiplicative feedback
Giuseppe Pesce, Austin McDaniel, Scott Hottovy, Jan Wehr & Giovanni Volpe
Nature Communications 4, 2733 (2013)
DOI: 10.1038/ncomms3733
arXiv: 1206.6271

Intrinsically noisy mechanisms drive most physical, biological and economic phenomena. Frequently, the system’s state influences the driving noise intensity (multiplicative feedback). These phenomena are often modelled using stochastic differential equations, which can be interpreted according to various conventions (for example, Itô calculus and Stratonovich calculus), leading to qualitatively different solutions. Thus, a stochastic differential equation–convention pair must be determined from the available experimental data before being able to predict the system’s behaviour under new conditions. Here we experimentally demonstrate that the convention for a given system may vary with the operational conditions: we show that a noisy electric circuit shifts from obeying Stratonovich calculus to obeying Itô calculus. We track such a transition to the underlying dynamics of the system and, in particular, to the ratio between the driving noise correlation time and the feedback delay time. We discuss possible implications of our conclusions, supported by numerics, for biology and economics.

Work Done by Rotational Force Fields published in J. Opt.

Influence of rotational force fields on the determination of the work done on a driven Brownian particle

Influence of rotational force fields on the determination of the work done on a driven Brownian particle
Giuseppe Pesce, Giovanni Volpe, Alberto Imparato, Giulia Rusciano & Antonio Sasso
Journal of Optics 13(4), 044006 (2011)
DOI: 10.1088/2040-8978/13/4/044006
arXiv: 1006.4534

For a Brownian system the evolution of thermodynamic quantities is a stochastic process, in particular the work performed on a driven colloidal particle held in an optical trap, changes for each realization of the experimental manipulation, even though the manipulation protocol remains unchanged. Nevertheless, the work distribution is governed by established laws. Here, we show how the measurement of the work distribution is influenced by the presence of rotational, i.e. nonconservative, radiation forces. Experiments on particles of different materials show that the rotational radiation forces, and therefore their effect on the work distributions, increase with the particle’s refractive index.

Non-conservative Forces in Optical Traps published in EPL

Quantitative assessment of non-conservative radiation forces in an optical trap

Quantitative assessment of non-conservative radiation forces in an optical trap
Giuseppe Pesce, Giorgio Volpe, Anna Chiara De Luca, Giulia Rusciano & Giovanni Volpe
EPL (Europhysics Letters) 86(3), 38002 (2009)
DOI: 10.1209/0295-5075/86/38002
arXiv: 0902.4178

The forces acting on an optically trapped particle are usually assumed to be conservative. However, the presence of a non-conservative component has recently been demonstrated. Here, we propose a technique that permits one to quantify the contribution of such a non-conservative component. This is an extension of a standard calibration technique for optical tweezers and, therefore, can easily become a standard test to verify the conservative optical force assumption. Using this technique, we have analyzed optically trapped particles of different size under different trapping conditions. We conclude that the non-conservative effects are effectively negligible and do not affect the standard calibration procedure, unless for extremely low-power trapping, far away from the trapping regimes usually used in experiments.

Actin-cytoskeleton Depolymerisation Detection in a Single Cell published in Opt. Express

Real-time actin-cytoskeleton depolymerization detection in a single cell using optical tweezers

Real-time actin-cytoskeleton depolymerization detection in a single cell using optical tweezers
Anna Chiara de Luca, Giovanni Volpe, Anna Morales Drets, Maria Isabel Geli, Giuseppe Pesce, Giulia Rusciano, Antonio Sasso & Dmitri Petrov
Optics Express 15(13), 7922—7932 (2007)
DOI: 10.1364/OE.15.007922

The cytoskeleton provides the backbone structure for the cellular organization, determining, in particular, the cellular mechanical properties. These are important factors in many biological processes, as, for instance, the metastatic process of malignant cells. In this paper, we demonstrate the possibility of monitoring the cytoskeleton structural transformations in optically trapped yeast cells (Saccharomyces cerevisiae) by tracking the forward scattered light via a quadrant photodiode. We distinguished normal cells from cells treated with latrunculin A, a drug which is known to induce the actin-cytoskeleton depolymerization. Since the proposed technique relies only on the inherent properties of the optical trap, without requiring external markers or biochemical sensitive spectroscopic techniques, it can be readily combined with existing optical tweezers setups.